Medicinal polyester plastic bottle processing technology

Polyester plastic bottle is currently one of the most important plastic packaging materials, mainly used for medicines, carbonated beverages, but also packaging alcoholic beverages, tea beverages, fruit juices, mineral water, edible oils, seasonings, cosmetics, pesticides and detergents And other liquid packaging. As a medicine packaging container. PET has a variety of advantages. First, PET bottles are lightweight and strong, and the strength and elasticity are significantly higher than those of plastic bottles made of other plastic materials. They can withstand considerable impact without damage, and are most suitable for thin, lightweight, High strength pharmaceutical bottles. In the case of the same drug volume, the PET bottle weighs only 1/10th of that of the glass bottle; for the same OD bottle, the PET bottle is easily 5 times the glass bottle. Transparent or opaque brown bottles can be made from PET stock. Medicinal PET bottles have good gas barrier properties. Among commonly used plastics, PET bottles have the most excellent barrier to water vapor and oxygen and can fully meet the special storage requirements for pharmaceutical packaging. PET bottles have excellent chemical resistance and can be used for packaging all substances except strong alkalis and some organic solvents. The recycling rate of PET resin is higher than that of other plastics. When it is burned as a waste, it has a low calorific value and is flammable and does not produce harmful gases. Food packaging made of PET meets the food hygiene requirements because PET resin is not only a harmless resin, but also a pure resin without any additives. It passed the fairly stringent food hygiene regulations including the United States, Europe and Japan. Inspection is considered as a qualified and safe packaging material for medicines and foods. 

Cript> First, the main processing technology of medicinal polyester bottles

1 The PET raw material used for bottle body blow molding is saturated linear thermoplastic polyester. The main application performance index is: the intrinsic viscosity (IV) should be controlled at 70-85 mL/g, so that blown bottles have high mechanical properties and transparency. It is used for stretch blow-molded bottle body (greater than 2L). The intrinsic viscosity of polyester raw material is 70-75 mL/g. Injectable plastic injection small-volume bottles are preferred to use higher intrinsic viscosity index for production. Since the selection of raw materials is correct or not, it affects the selection of molding process parameters in the production process and the quality of the bottles after molding. Therefore, in the production of medicinal PET bottles, the intrinsic viscosity, crystallization temperature, cooling rate, and orientation effects of the raw materials, etc. Process data is particularly important. This is because the polyester material is a crystallizable polymer whose crystallization rate is as small as 6 μm/min (max). That is, by controlling the conditions of the crystallization temperature and the cooling rate, the polyester bottle can be made amorphous or crystalline, and the crystal type and quantity can be changed. Polyester requires a crystallinity of about 30%. The orientation effect of the polyester raw material causes the polyester molecules to be arranged in an orderly manner and promotes crystallization. The crystals formed are called strain-inducing crystals, and the crystal grains thereof are small and do not refract light, so the PET bottles are oriented to make the bottles Transparent body. If you want to make the bottle hot-filled and can be used in the Pakistan-style sterilization treatment, it is also necessary to heat-set the partially oriented and oriented polyester so that it can be further crystallized to improve the heat resistance. Therefore, in the process characteristics of polyester raw materials, molecular crystallization and orientation are the key factors influencing the quality and performance of the stretch blowing polyester bottle forming process. 

2 Dehydration and drying of polyester materials

Since the polyester material is a hygroscopic polymer, it should be strictly dried to make its residual moisture content less than 0.005% before processing and molding. Polyester raw materials are dried using a desiccant drying system. Drying conditions can be selected as follows: drying temperature 140-180°C, air dew point 40°C, air volume 0.06 cmm/kgh. Drying time 4h. The mastery of these conditions should be noted: 1 When the air volume value is higher than 0.06 cmm/kgh, the operation range can be widened, the drying temperature can be lowered, and the energy consumption can be too high; 2 It is very important to ensure that the dew point is as low as possible. However, there is no problem with the dew point up to -10°C. However, the dew point of the air should also be strictly monitored. When there is a high dew point, it should be reduced in time. 3 Drying temperature is a key parameter. The optimum drying temperature can be determined by drying and measuring the intrinsic viscosity of the parison at various temperatures, typically 150-163°C. Drying temperature should be reduced to about 120 °C when shutting down; 4 longer drying time will reduce the intrinsic viscosity of polyester raw materials, a reasonable grasp of drying temperature is a key parameter, a slight increase in temperature will lead to a greater reduction in the intrinsic viscosity of polyester, so The drying time is as short as possible to broaden the operating range. During the drying process, due to the high drying temperature of the polyester, the hopper of the equipment should have good thermal insulation properties and adopt glass fiber as the heat insulation layer, and the dried polyester material should be prevented from contacting with the outside air because of the polyester raw material. Will quickly absorb the moisture in the air. For example, when the completely dried polyester raw material is exposed to air having a relative humidity of 35% to 40% for 12 minutes, the moisture content reaches 0.005%. 

Second, the pharmaceutical PET bottle molding method

PET bottles can be molded by extrusion blow molding and injection blow molding processes. Stretch blow molding is divided into one-step and two-step methods. In the one-step molding process, parison molding, cooling, heating, stretching and blow molding, and bottle removal are completed on one machine in turn. The step method uses an extrusion or injection molding parison, and the parison is cooled to room temperature to become a semi-finished product, and then the parison is sent to a reheat stretch blow molding machine to be a bottle body. That is, parison molding, stretching, and blow molding are performed on two machines, respectively. One-step injection molding of blow-molded PET bottles requires two injection molds and blow molds for injection blow-molding equipment. The injection mould is mainly composed of the mould cavity and the mandrel. The correctness of the selection of the dimension parameters of each part is the key to whether the bottle can be formed. Therefore, it is necessary to reasonably select the size parameters of the mould and the forming process. .

1 Height and Diameter Parameters of Injection Mold Blanks

The ratio of the height of the PET bottle to the diameter of the neck of the neck can determine the aspect ratio (L/D) of the parison to the mandrel. The length-to-diameter ratio of the mandrel should not exceed 10:1 in general because the mandrel is a cantilever beam in the parison mold and is subjected to a high injection pressure during mold filling. When the long diameter is large, the bending is large, which may cause uneven thickness distribution of the parison. However, the mold filling speed can be controlled by a program or the head of the mandrel can be temporarily fixed by a sliding top meter during filling to make the core. The rod is centered, and the aspect ratio of the mandrel is preferably large. The height of the parison is obtained by referring to the bottle height multiplied by the height coefficient, which is generally 92% to 95% of the height of the bottle body. In order to ensure a high transparency of the parison, after the melt is filled into the parison mold, the temperature must be reduced to 145° C. or less quickly, but higher than the glass transition temperature (82° C.) of the polyester material, and the glass is closer to vitrification. The temperature, the higher the transparency of the blown bottle. The parison mold cooling water temperature is as low as 10 to 35° C. to quickly cool the parisons, and also the continuous cooling of the mandrels by liquid or gas, wherein the air cooling can make the mandrels have a more uniform temperature distribution, and the cold air pressure is generally About 1MPa. 

2  injection molding parison blow ratio ratio 

Injection blow small volume PET bottles, the main direction of circumferential stretching occurs during injection blow, the smaller the axial stretch, the greater the blow ratio (the ratio of the bottle diameter to the diameter of the blank body), and the uneven wall thickness distribution. The greater the possibility, the uneven wall thickness at the curved part of the filter region of the bottle shoulder and the bottle body or the bottom of the bottle. Blowing ratio of small-capacity bottles is generally between 1.5 and 1.8. For the bottle body with an oval cross-section, if the ratio of the length of the ellipse ratio, that is, the length of the major and minor axes of the ellipse, is less than 1  5:1, a parison having a circular cross-section can be formed. When the ellipse ratio is not more than 2:1, the mandrel may be formed by using a mandrel having a circular cross section and an elliptical parison cavity. When the elliptic ratio is greater than 2:1, it is generally required that both the mandrel and the parison cavity are designed to be elliptical. With the increase of the elliptic ratio, the design difficulty and manufacturing cost of the parison mold are increased, generally not exceeding 3:1. 

3Injection of parison mouth and neck dimensions

The parison mouth diameter and thread size should be consistent with the bottle mouth thread size and match the cap thread size. Since there is no unified national standard for this, the size of the bottle mouth is determined based on the contents of the bottle body. When determining the size of the neck of the parison and the size of the cavity of the blow mold, the shrinkage of the body after molding should also be considered. The blowing pressure of the PET bottle in the parison was 1.2 MPa. Cooling water was used to cool the blow mold at a water temperature of 5 to 10° C. so that the shape could be rapidly cooled after the bad inflation. 

4PET injection blow molding mandrel function and its role

The role and function of the mandrel used in injection blow molding are mainly in five aspects: 1 to determine the shape of the molded parison and the inner diameter of the neck of the bottle body; 2 to remove the parison or the bottle body during the mechanical indexing process; 3 Mandrels are provided with air passages and air inlets and outlets for conveying compressed air to inflate the shaped body; 4 core rods can be circulated through the liquid or air to adjust the temperature of the parisons; 5 the depth of the core rod is set close to the mating surface. The 10mm groove makes the end of the parison wedge into the groove, avoiding the misalignment of the neck thread caused by the elastic shrinkage of the parison during the transfer from the parison forming station to the blow-molding station and the groove sealing Function to reduce the leakage of compressed air during inflation. 

5 Selection of length and diameter of mandrel

The length and diameter of the mandrel are mainly determined by the parison, and the diameter of the mandrel body is smaller than the inner diameter of the neck of the bottle body, so that the bottle body can be demoulded. However, the diameter of the mandrel should be as large as possible within the inner diameter of the bottleneck to avoid causing excessive blow-up ratio. The mandrel concentricity should be in the range of 0.05 to 0.08 mm in diameter. The diameter of the mandrel at the mouth of the bottle is determined by the outer diameter of the bottle mouth and the thickness of the bottle mouth. The range of the mandrel diameter is generally equal to the bottle mouth diameter equal to the bottle mouth Trail minus wall thickness twice. 

6 Determination of the distance between the bottom of the mandrel and the bottom of the parison

This distance dimension is the thickness of the bottom of the parison. Whether it is reasonable or not depends on whether the thickness of the bottom of the bottle meets the requirements. The commonly used calculation method is: the thickness of the parison bottom (B) is equal to the minimum thickness of the bottom (T) plus 0.1 times the weight of the bottle (W)/g. The material used for the core rod body is an alloy tool steel with a hardness of HRc52-54. Harder than the mold collar. The surface of the mandrel in contact with the melt is polished along the flow direction of the melt and plated with hard chrome to facilitate melt filling and mold release. In the blowing and stripping station of the PET bottle, the gas continues to circulate in the mandrel to ensure a more consistent temperature distribution of the mandrel. The temperature of each section of the mandrel is: 45-55° C. for the head (corresponding to the neck of the parison), 40-50° C. for the middle (corresponding body), and 23-35° C. for the tail. In the parison injection station, the temperature of the mandrel is at the upper limit of the above range due to the high melt temperature, and the temperature at the mandrel transfer to the demolding station is reduced to the lower limit due to internal cooling. After the bottle is ejected at the demolding station, the head of the mandrel is air-cooled from outside to reduce the temperature of the mandrel.